Date of Graduation

5-2014

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Brye, Kristofor R.

Committee Member

Fairey, Julian L.

Second Committee Member

Miller, David M.

Third Committee Member

Mason, Richard E.

Keywords

Applied sciences; Health and environmental sciences; Arsenic; Chromium; Extraction; Fly ash; Leaching; Selenium

Abstract

Selenium (Se) contamination can be a potential groundwater concern near un-lined coal ash landfills. Out of all the Environmental Protection Agency (EPA) priority and non-priority pollutants, Se has the narrowest range between what is considered beneficial and detrimental for aquatic and terrestrial organisms. The effects of ash type (i.e., fresh and weathered), water-extractant type (i.e., deionized water, rainwater, and groundwater), and extraction time (i.e., 2- and 6-hours) on Se, arsenic (As), and chromium (Cr) concentrations were investigated from Class C, subbituminous coal fly ash produced at the Flint Creek Power Plant located in Benton County, AR. Water-extractable Se concentrations differed (P = 0.03) between ash types across water-extractants, but were unaffected by extraction times. Unexpectedly, fresh ash water-extractable Se concentrations were below minimum detection limits (i.e., 2.0 µg L-1) for all treatments. In contrast, averaged over extraction times, the weathered ash water-extractable Se concentration was greatest (P < 0.05) with groundwater and rainwater, which did not differ and averaged 60.0 µg L-1, compared to extraction with deionized water (57.6 µg L-1). Selenite (Se4+) was greater (P < 0.001) in the fresh (3.85 mg kg-1) than in the weathered ash (0.70 mg kg-1), while selenate (Se6+) concentration was greater (P < 0.001) in the weathered (0.67 mg kg-1) than in fresh ash (0.48 mg kg-1). Results from this study indicate that environmental weathering of Class C, subbituminous fly ash promotes oxidation of selenite (Se4+), to the less toxic, but highly mobile selenate (Se6+). The formation of hydrated ettringite [Ca6Al2(SO4)3(OH)12 - 26H2O] and calcium selenite (CaSeO3) likely acted as a sink for weathered ash selenite (Se4+). Implications of this research include a better understanding of the past, present, and future environmental and health risk potential associated with the release of water-soluble Se, As, and Cr to aid in the development of sustainable fly ash management strategies.

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